Giant Step Forward in Generating Optical Qubits

Generation of complex entangled quantum states on an optical chip. (Source: UOPG)

Generation of complex entangled quantum states on an optical chip. (Source: UOPG)

The optical chip developed at INRS by Roberto Morandotti’s team overcomes a number of obstacles in the development of quantum computers, which are expected to revolutionize information processing. The inter­national research team has demonstrated that on-chip quantum frequency combs can be used to simulta­neously generate multi­photon entangled quantum bit (qubit) states.

Quantum computing differs fundamen­tally from classical computing, in that it is based on the gene­ration and processing of quits. Unlike classical bits, which can have a state of either 1 or 0, quits allow a super­position of the 1 and 0 states, both simulta­neously. Strikingly, multiple quits can be linked in so-called entangled states, where the mani­pulation of a single qubit changes the entire system, even if individual qubits are physically distant. This property is the basis for quantum information processing, aiming towards building superfast quantum computers and trans­ferring infor­mation in a completely secure way.

Morandotti has focused his research efforts on the realization of quantum components compatible with established techno­logies. The chip developed by his team was designed to meet numerous criteria for its direct use: it is compact, inex­pensive to make, compatible with electronic circuits, and uses standard tele­communication frequencies. It is also scalable, an essential charac­teristic if it is to serve as a basis for practical systems. But the biggest techno­logical challenge is the generation of multiple, stable, and control­lable entangled qubit states.

The generation of quits can rely on several different approaches, including electron spins, atomic energy levels, and photon quantum states. Photons have the advantage of preserving entan­glement over long distances and time periods. But genera­ting entangled photon states in a compact and scalable way is difficult. “What is most important, several such states have to be generated simulta­neously if we are to arrive at practical appli­cations,” added INRS research associate Michael Kues.

Roberto Morandotti’s team tackled this challenge by using on-chip optical frequency combs for the first time to generate multiple entangled quit states of light. As Michael Kues explains, optical frequency combs are light sources comprised of many equally-spaced frequency modes. “Frequency combs are extra­ordinarily precise sources and have already revolutionized metrology and sensing, as well as earning their dis­coverers the 2005 Nobel Prize in Physics.”

Thanks to these integrated quantum frequency combs, the chip developed by INRS is able to generate entangled multi-photon quit states over several hundred frequency modes. It is the first time anyone has demon­strated the simul­taneous generation of quit multi-photon and two-photon entangled states: Until now, integrated systems developed by other research teams had only succeeded in generating indi­vidual two-photon entangled states on a chip.

The results will provide a foundation for new research, both in integrated quantum photonics and quantum frequency combs. This could revolu­tionize optical quantum techno­logies, while at the same time main­taining compati­bility with existing semi­conductor chip technology. (Source: INRS)

Reference: Christian Reimer et al.: Generation of multi photon entangled quantum states by means of integrated frequency combs, Science, 351, 1176-1180, DOI: 10.1126/science.aad8532 

 Link: Nonlinear Photonics Group (R. Morandotti), Énergie Matériaux Télécommunications, Institut National de la Recherche Scientifique, Varennes, Québec, Canada

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